1. Field of the Invention
This invention relates to a waveguide device having a mode filter function of selectively transmitting either of TE mode polarized light and TM mode polarized light, and a method of producing the same.
2. Description of the Related Art
Conventionally, a method called `photobleaching` by photoirradiation has been proposed as one method of producing a channel-type waveguide (see Electronics Lett., 26, 1990, page 379). This is a method in which, with a photomask placed, light is irradiated on a part deposited on a substrate and becoming a waveguide layer, thereby decreasing the refractive index of the light irradiated part and producing a waveguide provided with a core which confines and propagates light. This method relates to a waveguide layer constituted by an optically isotropic material, and an analysis of optically anisotropic material has not been attempted yet. Application of this method to a waveguide device serving as a mode filter or the like has not been attempted, either.
Moreover, a waveguide device disclosed as the prior art in FIG. 4 of Japanese Unexamined Patent Publication (KOKAI) No.62-299913 has been known as a conventional waveguide device functioning as a mode filter. In this waveguide device, a metal is placed on a core of a glass waveguide, or an optically anisotropic crystal (e.g., calcite, a Nb.sub.2 O.sub.5 film) which has a different refractive index from that of a core of a glass waveguide is placed on the core of the glass waveguide. Because the optically anisotropic crystal which has a different refractive index from that of the core of the glass waveguide is thus placed on the core of the glass waveguide, there have been a problem in which steps become complicated to produce this device with precision. Further, this art is under restrictions in which refractive indices of optically anisotropic crystals are constant and crystals with desired anisotropic refractive indices cannot be always obtained.
The art shown in FIGS. 1 to 3 of the above Japanese unexamined patent publication was developed in an attempt to dissolve the above problems, and is that a film having an equal or substantially equal refractive index to that of a core of a waveguide is placed in the neighborhood of the core of the waveguide, so that either of TE mode polarized light and TM mode polarized light is irradiated and the other is propagated.